The present invention relates to a device for transferring and inspecting groups of cigarettes destined for the wrapping line of a packer.
Groups of cigarettes are transferred as a rule in substantially parallelepiped receptacles affording respective compartments and anchored at constant pitch to an infeed conveyor of the packer machine.
The conveyor, which is driven by a shaft of the machine, consists in an endless belt looped around return rollers. The cigarettes making up each group in a relative compartment are disposed transversely to the feed direction followed by the belt and, in the case of a group of twenty, for instance, arranged in three layers comprising two layers of seven cigarettes each, with a third layer of six cigarettes interposed quincuncially between the two layers of seven.
Thus, each single cigarette of the group occupies a predetermined fixed position internally of the respective compartment.
It is often the case that the group occupying a given compartment will be incomplete, or include at least one substandard cigarette, for example with a shortage of tobacco filler at the one end, or with the filter tip missing from the other end.
To enable the detection and subsequent rejection of defective groups, the machine is equipped with an inspection device, for example of optical type employing photocells, installed at a predetermined inspection position along the path followed by the conveyor. The device in question, for example as described in U.S. Pat. No. 4,511,045, is able to scan the single compartments passing in succession through the inspection position and verify that each one contains the correct number of cigarettes, also that the bare end faces of the cigarettes are properly filled and the opposite ends are furnished with filters.
The inspection of each group and of the single constituent cigarettes occurs with the conveyor in motion and is enabled by a succession of machine cycle signals, each synchronized with a moment in which the inspection device scans the position occupied by the end face of a cigarette making up the group.
The cyclical enabling signals are generated by devices coupled to the shaft of the machine which, to reiterate, is connected mechanically to the conveyor carrying the fixed receptacles.
Signals resulting from the inspection of each compartment are relayed to a memory device and utilized when appropriate to activate a device, positioned along the path of the conveyor, by which the defective groups are ejected.
Self-evidently, the correct operation of an inspection device as described above is dependent on permanently stable timing between the machine shaft, with which the devices emitting the cyclical enabling signals are rigidly associated, and the looped conveyor carrying the receptacles in which the groups of cigarettes are located, or in short, between the enabling signals and the positions of the single cigarettes within the inspected groups.
It has been found however, that as the system becomes affected by backlash, attributable for example to wear in the mechanical linkage between the drive shaft and the conveyor belt loop, or to slack in the belt itself, the aforementioned timing is gradually lost, and the signals emitted by the inspection device no longer reflect the condition of the cigarettes making up the group, resulting as they do from scans effected on positions no longer aligned with the end faces of the cigarettes.
This deleterious loss of timing can also occur as a result of the receptacles not being fixed rigidly to the conveyor, but mounted slidably both relative to the belt and in relation one to another, as is the case with a device of the type described, for example, in patent EP 1 152 944.
As a result of the aforementioned timing being lost, it can happen both that groups of cigarettes including defective items are not ejected, and that groups of perfectly good cigarettes will be ejected in error.
The object of the present invention is to provide a transfer and inspection device in which all of the aforementioned drawbacks are overcome.